The present invention relates generally to textile warp knitting machines, weaving machines and other textile processing machines wherein yarn is wound about and supplied from a warp beam. More particularly, the present invention relates to a method and apparatus for monitoring the depletion of yarn wound about a warp supply beam for stopping operation of the associated textile processing machine in advance of full depletion of yarn from the beam.
In various textile fabric forming equipment, in particular warp knitting machines and weaving machines, yarn is supplied to the machine from one or more warp beams or spools about which a plurality of yarns are wound in side-by-side relation to be simultaneously fed to the machine by beam rotation synchronously with the rate of production of the associated machine. As is widely appreciated within the textile industry, a warp beam of this type should not be permitted to fully deplete whereby the trailing ends of the yarns would be lost into the associated machine, disadvantageously terminating its continuous operation, requiring re-setup of the machine, and in many cases presenting a significant risk of damage to the yarn manipulating instrumentalities of the machine due to continuing machine operation without a supply of yarn.
Accordingly, conventional practice is to stop operation of the textile machine shortly in advance of full warp beam depletion, for replacement of the depleted beam with a full warp beam. Conventionally, the determination of when to stop the machine for exchange of a depleted warp beam is made by a machine operator merely by visually monitoring the gradual depletion of yarn from the beam. As will be readily understood, this technique is inherently inexact. Since all warp yarn remaining on the depleted warp beam when taken out of service is discarded as waste, it is of course desirable to allow the beam to deplete as much as possible before replacement. On the other hand, since the overriding concern in all cases is to avoid complete depletion of yarn from the beam, an operator must exercise caution and good judgment, a high yarn waste factor resulting from premature beam replacement being substantially less disadvantageous than the aforementioned problems resulting from complete depletion of the beam. Proper exercise of the operator's judgment is a particularly difficult problem with machines which operate at relatively high warp yarn feeding rates, such as conventional warp knitting machines, so that the yarn waste factor in the operation of such machines is often relatively high.
U.S. Pat. No. 3,751,937 discloses a means of automatically detecting the depletion of a warp beam in a textile warp knitting machine. According to this patent, a strip of adhesive tape is secured transversely across several of the warp yarns on a warp beam at a location near the yarn ends when first wound onto the beam. An associated sensor is provided for detecting the tape as the warp beam is depleted to thereby sense the impending exhaustion of the beam. A switch is operated in response to the sensor to terminate operation of the machine when the sensor detects the tape. While this invention offers advantages over the conventional technique aforedescribed of an operator manually stopping the machine based upon a visual monitoring of the warp beam, the invention is also disadvantageous in that it requires special steps in the original preparation of the warp beam and the adhesive from the tape may deleteriously affect the yarns to which the tape is adhered. It is unknown whether this invention has achieved any reasonable degree of commercial acceptance and use.